This invention is directed to a thermoplastic nonwoven web of fibers having a cyclodextrin compound chemically reacted with the thermoplastic polymer. The chemical reaction imparts durable hydrophilic properties to the fiber surfaces.
Water-permeable nonwoven fabrics, porous films, open-celled foams, and other layer materials and their manufacture have been the subject of extensive development resulting in a wide variety of materials for numerous applications. For example, nonwovens of light basis weight and open structure are used in personal care items such as disposable diapers as liner fabrics that provide dry skin contact but readily transmit fluids to more absorbent materials which may also be nonwovens of a different composition and/or structure. Nonwovens of heavier weights may be designed with pore structures making them suitable for filtration, absorbent and barrier applications such as wrappers for items to be sterilized, wipers or protective garments for medical, veterinary or industrial uses. Even heavier weight nonwovens have been developed for recreational, agricultural and construction uses. Water-permeable porous thermoplastic films are also employed in some of these applications, and may be combined with nonwoven webs. Open-celled foams are also useful in some applications.
It is not always possible to efficiently produce a porous, water-permeable layer material having all the desired properties as formed, and it is frequently necessary to treat the material with a surfactant to improve or alter surface properties such as wettability by one or more fluids, repellency to one or more fluids, electrostatic characteristics, conductivity, and softness, to name just a few examples. Conventional surfactant treatments involve steps such as dipping the substrate in a treatment bath, coating or spraying the substrate with the treatment composition, and printing the substrate with the treatment composition. For cost and other reasons it is usually desired to use the minimum amount of treatment composition that will produce the desired effect with an acceptable degree of uniformity.
For many thermoplastic layer material end use applications, it is desirable to reduce, prevent, or eliminate odors. For diapers and other incontinence products, it is desirable to reduce or eliminate the odor of ammonia which is present in urine. For feminine hygiene products, it is desirable to reduce or eliminate the odor of triethylamine. Other common odor-producing substances include isovaleric acid, dimethyl disulfide, and dimethyl trisulfide.
Odor control agents include odor inhibitors, odor absorbers, and other compounds which reduce, prevent, or eliminate odors. Odor inhibitors prevent the odor from forming. For example, U.S. Pat. No. 4,273,786 to Kraskin teaches the use of an aminopolycarboxylic acid compound for inhibiting the formation of ammonia from urea in urine. Odor absorbers and adsorbers remove odor after it is formed. Examples of odor control agents that remove odor by absorption or adsorption include activated carbon, silica, and cyclodextrins.
Typical odor control agents based on cyclodextrins cannot easily be applied from aqueous solutions to water-permeable thermoplastic substrates such as polyolefin nonwoven fabrics, porous films, and open-celled foams because the surface tension of these solutions is too high to wet out the hydrophobic substrate. Personal care products such as diapers and feminine care pads typically contain polyolefin nonwoven fabrics and/or other porous thermoplastic cover layers. Therefore, typical odor control agents cannot usually be applied to the porous thermoplastic components of personal care products. Instead, these odor control agents are usually introduced as powders to the product, which has several drawbacks. For example, placement and containment of the powder in the product can be troublesome. More importantly, powders do not present optimum surface area for odor absorption due to a rather low surface to volume ratio. Therefore, more odor control agent will be needed if in powder form. Furthermore, odor control and hydrophilic modifiers applied in powder form, or as surface treatments, are often not desirable and can be washed away.
There is a need or desire for odor absorbing compounds, hydrophilic modifiers, antistatic agents, and the like which can be applied to a water-permeable hydrophobic (e.g., thermoplastic) substrate in a manner which optimizes the coating over the target surface area, and which prevents easy washing/removal of the compounds.
Nonwoven polymer-based battery separators are also known in the art. U.S. Pat. No. 5,589,302, issued to Degen et al., discloses a battery separator including a nonwoven web of fibers having a mean diameter of about 15 microns or less, and a graft polymerized monomer on the surface of the nonwoven web which renders the web spontaneously wettable by an alkaline electrolyte. The nonwoven web includes a mixture of two polymers having different melting points. The monomers suitable for grafting include vinyl sulfonic acid, vinyl phosphonic acid, and acrylic and methacrylic acid and hydroxyl functional derivatives thereof. The grafting is effected by irradiating the nonwoven web in the absence of oxygen, before or during exposing the web to a solution of the monomer. The use of E-beam radiation is disclosed.
One disadvantage of the above battery separators is that some of the residual monomer and ungrafted oligomers may leach out during prolonged exposure to the battery electrolyte. This leaching contaminates the electrolyte, and is detrimental to the performance of the battery cell. The leaching is largely attributable to: a) incomplete chemical reactions, b) competing homopolymerization reactions, and c) residual catalysts. There is a need or desire for a polymeric nonwoven web-based battery separator which has a greater affinity for the monomer, and which contains less unreacted monomer. There is also a need or desire for a process of making a battery separator, which facilitates a more complete reaction between the wettable monomer and/or polymer and the polyolefin fibers.
The present invention is a thermoplastic water-permeable layer material, such as nonwoven fibrous web, in which the thermoplastic polymer has been chemically reacted (e.g., grafted) with a cyclodextrin compound. Suitable cyclodextrin compounds include methacryloyl-R-cyclodextrins, where R is an alkyl group having 2 to 20 carbon atoms; acryloyl-R-cyclodextrins, where R is an alkyl group having 1 to 20 carbon atoms; alkenyl succinylated cyclodextrins, where the alkenyl group has 2 to 20 carbon atoms; and the like. The cyclodextrin compounds can have a degree of substitution ranging from 0.1 to 7. The compounds can be based on any known cyclodextrin having 6 to 12 glucose units arranged in a ring, including without limitation an alpha-cyclodextrin (having 6 glucose units), a beta-cyclodextrin (having 7 glucose units), a gamma-cyclodextrin (having 8 glucose units), or a combination including one or more of the foregoing.
The cyclodextrin-modified nonwoven web has durable hydrophilic properties and odor control which are useful in personal care absorbent articles and protective garments. The cyclodextrin-modified nonwoven web can also be used for a battery separator, for selective filtration of organic molecules, and as a delivery system for drugs, fragrances, bioactive agents, catalysts, dyes, brighteners, and other compounds. When used as a battery separator, the grafted substrate remains hydrophilic and functional in a highly oxidizing medium, for instance, a 40% potassium hydroxide aqueous solution. When used as a filter or delivery system, small molecules can be temporarily hindered or trapped inside the cyclodextrin cavities, each of which is formed by a ring of glucose units. Because of the chemical reaction, the improved properties of the nonwoven web are durable, and the cyclodextrin compound cannot be easily washed away or otherwise removed.
With the foregoing in mind, it is a feature and advantage of the invention to provide a cyclodextrin-modified thermoplastic water-permeable layer material, such as a fibrous nonwoven web, in which a cyclodextrin compound is chemically reacted with the thermoplastic polymer.
It is also a feature and advantage of the invention to provide a method of making the cyclodextrin-modified water-permeable layer material.